The difference is in the media they replicate. Drawing uses lines and some shading and the motions (whether with a trackpad, mouse, or tablet) are similar to drawing on paper. Painting uses shading and broad, smoother strokes, although it may feel like drawing, depending on the program one uses. Most digital art, in my (limited) experience is a combination of the two. Ultimately, though, it comes down primarily to what the finished product looks like.
I've no idea what does it mean painting or drawing in DIGITAL:/ If I use simple round brush, just change its size, is it a painting or drawing? I've read somewhere(another Deviat's opinion), painting is when you use special brusches (e.g. special fur brush), but I've no idea...
Technically...if you refer to "drawings" as those digital works which are either line-art, or are made in the way of or made to look like they were drawn with pencils or pens, and not solid-color paint.
I imagine them to be the same, except maybe for linearts (but it seems strange to make a category just for lineart). I would put them all in the same "digital paintings/drawings" category.
In traditional art, it's not about the look of the finished product but the technique. Working with dry media is quite different from wet media, even if the results can look similar. In digital art it's the opposite. The technique is alway either mouse or stylus, and everyone tries to classify it by the look of the finished product, which is... tricky, to say the least.
I guess it all comes down to whether or not you choose to label/categorize your work in relation to the actions you took to create it, by the materials used, or by the end result. As someone else pointed out below, a person can start with a simple line sketch ( which would be the action of drawing ) but then end up using painting technique to complete the piece and the end result for most would be considered a painting. However, if it's combined digital drawing/painting techniques, it would not be considered mixed media because the media is still all digital.
I've always thought that with the advancement/creation of all of this new technology that the creators should have taken a little time to come up with a new set of terms for digitally created work. I think it would have probably resolved a lot of the confusion about these issues now. Drawing is an action, and since you do use a pen on digital tablet to commit the act of drawing, then it makes sense to have the term digital drawing. The digital painting term has always confused me though. There isn't any paint involved, and I'd imagine that if you wielded your pen on your tablet like a painter often does with a brush on canvas, you'd probably ruin your tablet right quick. So then what really makes a digital painting a " painting " ? The definition of painting does not imply the inclusion or exclusion of linework or shapes, etc. It defines it as the act of applying paint to a surface with a brush ( or other tool ) or a picture or design created in paint. Neither of these apply to the digital illustrations that are currently labeled as digital paintings because they don't contain any actual " paint " in their creation. I've often wondered why they just didn't come up with a whole new term for this...I mean, if you can create the tech to make such masterpieces, surely you can take a few days to come up with a new term for it that makes sense so as avoid confusion about it.
Here is a question to confuse you even more....I have at times, watered down watercolor paint and used my dip pen to draw with it. So...is it a drawing or a painting? lol....this very confusion for me has kept me from submitting work because I really didn't know which category these drawing/paintings belonged in.